CHICAGO, Illinois, has been struck by an intense ‘polar vortex’ storm which has seen temperatures plummet to unprecedented levels and claimed 12 lives.

The brutally cold weather is due to let up a bit by the end of the week. But the historic cold has bitten through the region, with frigid air and wind chills stretching up to Maine. And as millions grapple with frigid temperatures, at least 12 deaths have been linked to this week's extreme weather.